Transformers often include a core and coil assembly formed from a pair of coils interconnected by a conductive core. A three phase transformer includes three coils with multiple cores. The core and coil assembly may be positioned in a tank that is filled with a dielectric fluid. The dielectric fluid serves to cool the assembly and electrically isolate the core and coil assembly from the tank.
Insulation used in the transformer core and coil assembly typically is constructed using kraft or cotton-based pressboard, which is known to degrade over time as a function of temperature. This insulation normally is made from multiple individual pieces that may require cutting to the correct size. Also, the insulation needs to be thoroughly dried prior to filling the tank with dielectric fluid because moisture contributes to and increases the degradation rate, especially when combined with heat. Typical kraft-based pressboard materials absorb moisture in a range from approximately 3% to 10%, or more, based on the length of exposure to humidity. This moisture should be removed to a level of approximately 1% prior to filling the transformer with dielectric fluid. Current kraft or cotton-based pressboard material absorbs moisture and degrades rapidly at temperatures from 130° C. to 170° C. Further moisture developed during the degradation process of kraft or cotton-based pressboard, accelerates aging and degradation of the pressboard.